FRANK Solutions for Class 9 Chemistry Chapter 9 - Study of the First Element - Hydrogen

Chapter 9 - Study of the First Element - Hydrogen Exercise 146

Question 1

(a) Write the symbol and molecular formula of hydrogen.
(b) What is the difference between 2H and H₂?
(c) Who gave hydrogen its name and why?

Solution 1

(a) Symbol of hydrogen is 'H' and its molecular formula is H₂.
(b) 2 H means 2 atoms of hydrogen while H₂ means one molecule of hydrogen.
(c) Lavoisier gave "Hydrogen" its name because it means water product.

Question 2

(i) Write balanced equation of the reaction in the preparation of hydrogen from a solution of potassium hydroxide.
(ii) Describe briefly, with equations, the Bosch Process for the large scale production of hydrogen.
(iii) Account for the following facts:
(a) Though lead is above hydrogen in the activity series, it does not react with dilute hydrochloric acid or dilute sulphuric acid.
(b) Potassium and sodium are not used to react with dilute hydrochloric acid or dilute sulphuric acid in the laboratory preparation of hydrogen.

Solution 2

Question 3

Name the various sources from which hydrogen can be obtained.

Solution 3

Hydrogen is found in free state as well as in combined  state.
1.In free state, it is found in traces in the earth's crust and atmosphere. On the sun and bright stars, hydrogen is very abundant.It is suggested that the source of sun's energy is fusion of hydrogen to helium.
2.In combined state it is found in the compounds like water, acids, organic materials and minerals. Natural gas coming out from oil wells, coal mines and volcanoes invariably contains this gas.

Question 4

How does hydrogen resemble the alkali metals (Group 1)?

Solution 4

Hydrogen resembles the alkali in following manner-
(i) Electronic configuration-Hydrogen as well as alkali metals have one electron in their valence shell.
H (1) = 1      ; Li(3)= 2, 1   ; Na(11) =2, 8, 1
(ii) Ion formation-Hydrogen loses one electron to form H⁺ ion like the alkali metals which form Li⁺, Na⁺, K⁺ etc.
(iii) Valency electrons-Like alkali metals, hydrogen exhibit valency of one in its compounds , as it has only one electron in its outermost shell.
(iv) Combination with non-metals-Like alkali metals, hydrogen combines with non-metals such as oxygen, chlorine and sulphur forming their oxides, chlorides and sulphides respectively.
(v) Reducing action-Like alkali metals, hydrogen is also a very good reducing agent.

Question 5

What is the justification for hydrogen being placed in the group of halogens in the periodic table.

Solution 5

Hydrogen resembles the alkali in following manner-
(i) Electronic configuration-All the halogens have seven electrons in their outermost shell and need just one more electron to attain stable inert gas configuration. Similarly, hydrogen with one electron in its outermost shell requires one electron to attain a stable inert gas(Helium) configuration.
(ii) Valency-Hydrogen and halogen both show a valency of one.
(iii) Non-metals-Hydrogen is non-metallic like halogen.
(iv) Atomicity-Hydrogen as well as halogens are diatomic gases, e.g.H₂,Cl₂.Br₂ etc.
(v) Ion formation-Halogens have a strong tendency to gain an electron to form halide ions.In similar way, hydrogen shows tendency to gain one electron to form hydride ion (H^-).

Question 6

How hydrogen can be prepared with zinc using acid and alkali? Give an equation in each case.

Solution 6

Question 7

Why following metals are not suitable for the laboratory preparation of hydrogen?
(i) Calcium
(ii) Iron
(iii) Aluminium
(iv) Sodium

Solution 7

Question 8

For the laboratory preparation of hydrogen,give the following:
(i) Reactants used
(ii) Reaction
(iii) Procedure
(iv) Complete labelled diagram
(v) Method of selection
(vi) Drying agent for gas

Solution 8

Question 9

What are the impurities present in the hydrogen gas obtained in the laboratory by dilute H₂SO₄ and granulated zinc? How are they removed?

Solution 9

Hydrogen gas  obtained in the laboratory by dilute H2SO4 and granulated zinc
have following impurities-
(i) Hydrogen sulphide (H₂S),
(ii) Sulphur dioxide (SO₂),
(iii) Oxides of nitrogen,
(iv) Phosphine (PH₃),
(v) Arsine (AsH₃),
(vi) Carbon dioxide, Nitrogen oxides,
(vii) Water vapour
They are removed by passing through-
(i) Lead nitrate solution-It absorbs H₂S.
(ii) Silver nitrate solution (AgNO₃)-It absorbs PH₃, AsH₃
(iii) Caustic potash (solid KOH)-It absorbs CO₂, SO₂, oxides of nitrogen
(iv) Anhydrous calcium chloride or P₂O₅-It absorbs moisture.

Question 10

(a) Write two equations for the reactions in which hydrogen is used as a reducing agent.
(b) Which of the following metal oxides cannot be reduced to metal by hydrogen?
CuO, Ag₂O, MgO, PbO

Solution 10

Chapter 9 - Study of the First Element - Hydrogen Exercise 147

Question 1

(a) Place the metals calcium, iron, magnesium and sodium in order of their reactivity with water, placing the most active first. Write the equation for each of the above metals which react with water.
(b) Why is copper not used to prepare hydrogen by the action of dilute HCl or dilute H₂SO₄ on the metal?

Solution 1

Question 2

Thin strips of three different metals A, B and C are known to be magnesium, copper and iron respectively.
(a) Write down what happens when the metals are treated as follows:
(i) When each metal is heated.
(ii) When each metal is heated with dilute HCl.
(iii) When each metal is added to an aqueous solution of zinc sulphate
(b) Arrange these metals in the descending order of their activities.

Solution 2

Question 3

Fill in the blanks:
(a) Vegetable oil can be changed into a solid by the use of a ______ catalyst and the ______ element.
(b) A metal ______ hydrogen in activity series gives hydrogen with ______ acids.
(c) Hydrogen form ______ bonds with strongly ______ elements.
(d) When CuO reacts with hydrogen, ______ is reduced and ______ is oxidised to ______.
(e) Water gas is a mixture of ______ and ______.
(f) Hydrogen gas is liberated by the action of aluminium with concentrated solution of ______.
(g) The hydrogen at the moment of its formation is called ______.
(h) When hydrogen burns ______ is produced.

Solution 3

(a) Nickel, hydrogen
(b) above, dilute mineral
(c) covalent, electronegative
(d) CuO, hydrogen, water
(e) CO, H₂
(f) alkali
(g) nascent hydrogen
(h) water

Question 4

Indicate which of the following statements are true and which are false:
(a) Hydrogen gas is easily liquefiable.
(b) Hydrogen is combustible as well as supporter of combustion.
(c) Anhydrous calcium chloride is used to dry hydrogen gas.
(d) The reaction between hydrogen and oxygen is exothermic.
(e) Zinc gives hydrogen when reacted with dilute HCl and conc. NaOH.
(f) The position of hydrogen is not fixed in periodic table.
(g) Magnesium with very dilute HNO₃ produces hydrogen.
(h) Occluded hydrogen is less active than ordinary hydrogen.

Solution 4

(a) False
(b) False
(c) True
(d) True
(e) True
(f) True
(g) True
(h) False

Question 5

Give reasons:
(a) Hydrogen is collected by the downward displacement of water and not by air,even though it is lighter than air.
(b) Apparatus for the laboratory preparation of hydrogen should be air tight and away from the flame.
(c) Nitric acid and hot concentrated H₂SO₄ are not used in the preparation of hydrogen.
(d) A large piece of sodium should not be placed in water.
(e) Na, K and Ca cannot be used to prepare hydrogen from acids.
(f) In the laboratory preparation of hydrogen zinc granules are preffered over pure zinc metal.
(g) In Bosch process, steam should not be passed over white coke for a long time.
(h) When a burning splinter is introduced into a jar of hydrogen, the splinter gets extinguished.
(i) Hydrogenated vegetable fats are not advised to be used in preparation of foodstuffs.
(j) Though hydrogen is the lightest element it is not used in weather ballons.
(k) Lead is not used to prepare hydrogen from acids.

Solution 5

Chapter 9 - Study of the First Element - Hydrogen Exercise 148

Question 1

Name the products obtained when hydrogen is
(a) passed over heated copper oxide.
(b) passed over heated sodium.

Solution 1

Question 2

How combination of hydrogen with chlorine is affected by sunlight?

Solution 2

Question 3

Explain the following terms:
(a) Occlusion
(b) Hydrogenation
(c) Nascent hydrogen

Solution 3

Question 4

How is hydrogen prepared in laboratory? List five precautions to ensure safe preparation and collection of the gas? How would you confirm that the gas collected is hydrogen?

Solution 4

Some pieces of zinc granules are placed in Woulfe's bottle and the apparatus is made in air tight. Now dilute sulphuric acid is poured through the thistle funnel.
Observation: The reaction takes place at room temperature even without heating. A brisk effervescence with the evolution of gas is seen inside the bottle.
If burning candle is brought near the bubbles of hydrogen gas, they explode.This proves that bubbles were full of hydrogen gas and they move up in the air because they are lighter than air.

Question 5

State the reason of use of hydrogen in
(a) meteorological balloons
(b) in metallurgy
(c) in fuel
(d) in making fertilizers

Solution 5

(a) Meteorological balloons - The low density and high lifting power of hydrogen made it useful in meteorological balloons used for studying air currents and weather conditions. However, due to its highly inflammable nature it has been replaced by helium which has a lifting only slightly less than that of hydrogen.
(b) In metallurgy - Hydrogen acts as a very good reducing agent. It is used to obtain metals by reducing their oxides.
(c) In fuel - Hydrogen has very high heat of combustions, therefore it is used as fuel  in the form of coal gas, water gas and liquid hydrogen(for rocket propulsion).
(d) In making fertilizers - A large quantity of hydrogen is used in the manufacture of ammonia by Haber process. Ammonia is used in manufacture of HCl and methyl alcohol.

Question 6

Give one example of a reaction in which hydrogen acts (a) as an oxidizing agent (b) as a reducing agent.

Solution 6